Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)

Abstract

We fit various colour-magnitude diagrams (CMDs) of the Galactic globular clusters NGC\,6397 and NGC\,6809 (M55) by isochrones from the Dartmouth Stellar Evolution Database (DSED) and Bag of Stellar Tracks and Isochrones (BaSTI) for $\alpha$-enhanced [$\alpha$/Fe]$=+0.4$. For the CMDs, we use data sets from {\it HST}, {\it Gaia}, VISTA, and other sources utilizing 32 and 23 photometric filters for NGC\,6397 and NGC\,6809, respectively, from the ultraviolet to mid-infrared. We obtain the following characteristics for NGC\,6397 and NGC\,6809, respectively: metallicities [Fe/H]$=-1.84\pm 0.02\pm 0.1$ and $-1.78\pm 0.02\pm 0.1$ (statistic and systematic uncertainties); distances $2.45\pm 0.02\pm 0.06$ and $5.24\pm 0.02\pm 0.18$ kpc; ages $12.9\pm 0.1\pm 0.8$ and $13.0\pm 0.1\pm 0.8$ Gyr; reddenings $E(B-V)=0.178\pm 0.006\pm 0.01$ and $0.118\pm 0.004\pm 0.01$ mag; extinctions $A_{\mathrm{V}}=0.59\pm 0.01\pm 0.02$ and $0.37\pm 0.01\pm 0.04$ mag; extinction-to-reddening ratio $R_{\mathrm{V}}=3.32_{-0.28}^{+0.32}$ and $3.16_{-0.56}^{+0.66}$. Our estimates agree with most estimates from the literature. BaSTI gives systematically higher [Fe/H] and lower reddenings than DSED. Despite nearly the same metallicity, age, and helium enrichment, these clusters show a considerable horizontal branch (HB) morphology difference, which must therefore be described by another parameter. This parameter must predominantly explain why the least massive HB stars (0.58-0.63 solar masses) are only found within NGC 6809. Probably they have been lost by the core-collapse cluster NGC\,6397 during its dynamical evolution and mass segregation. In contrast, NGC\,6809 has a very low central concentration and, hence, did not undergo this process.

19 figures. arXiv admin note: text overlap with arXiv:2211.12684

References in corpus (36)

• Gaia Data Release 3: Summary of the content and survey properties
• The Dartmouth Stellar Evolution Database
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Gaia Early Data Release 3: Photometric content and validation
• Improving PARSEC models for very low mass stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• Gaia EDR3 view on Galactic globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• SkyMapper Southern Survey: Second Data Release (DR2)
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• The White Dwarf Cooling Sequence of NGC6397
• Homogeneous photometry VII. Globular clusters in the Gaia era
• Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function
• A Multi-Band Catalog of 10978 Star Clusters, Associations and Candidates in the Milky Way
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIII. Proper-motion catalogs and internal kinematics
• Modeling Thermal Dust Emission with Two Components: Application to the Planck HFI Maps
• Synthetic Stellar Photometry - II. Testing the bolometric flux scale, and tables of bolometric corrections for the Hipparcos/Tycho, Pan-STARRS1, SkyMapper and JWST systems
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• Sodium abundances of AGB and RGB stars in Galactic globular clusters II. Analysis and results of NGC 104, NGC 6121 and NGC 6809
• The helium abundance in the metal-poor globular clusters M30 and NGC6397
• Multiple populations in massive star clusters under the magnifying glass of photometry: Theory and tools
• Multiple stellar populations in Asymptotic Giant Branch stars of Galactic Globular Clusters
• BALRoGO: Bayesian Astrometric Likelihood Recovery of Galactic Objects -- Global properties of over one hundred globular clusters with Gaia EDR3
• M13 multiple stellar populations seen with the eyes of Strömgren photometry
• Far-Ultraviolet Observation of the Globular Cluster NGC 6397
• Isochrone fitting of Galactic globular clusters -- II. NGC6205 (M13)
• Isochrone fitting of Galactic globular clusters -- III. NGC\,288, NGC\,362, and NGC\,6218 (M12)
• Probing Mass Segregation in NGC 6397
• Isochrone fitting of Galactic globular clusters -- IV. NGC6362 and NGC6723
• A ground-based proper motion study of twelve nearby Globular Clusters
• Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. II. Application to the Colour-Magnitude Diagrams of the Globular Clusters 47 Tuc, NGC 6362, M5, M3, M55, and M92
• A time-series VI study of the variable stars of the globular cluster NGC 6397
• A Three-Dimensional Analytical Model of the Interstellar Extinction within the Nearest Kiloparsec

Cited by in corpus (4)

• New Interstellar Extinction Maps Based on Gaia and Other Sky Surveys
• A combined study of thermohaline mixing and envelope overshooting with PARSEC: Calibration to NGC 6397 and M4
• Stellar evolution and axion-like particles: new constraints and hints from globular clusters in the GAIA DR3 data
• Synthetic stellar spectra to study multiple populations in globular clusters: an extended grid and the effects on the integrated light